U.S. patent application number 13/688032 was filed with the patent office on 2013-06-27 for lithium-titanium complex oxide, and battery electrode and lithium ion secondary battery containing same.
This patent application is currently assigned to TAIYO YUDEN CO., LTD.. The applicant listed for this patent is TAIYO YUDEN CO., LTD.. Invention is credited to Daigo ITO, Chie KAWAMURA, Masaki MOCHIGI, Toshiyuki OCHIAI, Yoichiro OGATA, Toshimasa SUZUKI, Akitoshi WAGAWA.
Application Number | 20130161558 13/688032 |
Document ID | / |
Family ID | 48637974 |
Filed Date | 2013-06-27 |
United States Patent
Application |
20130161558 |
Kind Code |
A1 |
KAWAMURA; Chie ; et
al. |
June 27, 2013 |
LITHIUM-TITANIUM COMPLEX OXIDE, AND BATTERY ELECTRODE AND LITHIUM
ION SECONDARY BATTERY CONTAINING SAME
Abstract
A lithium-titanium complex oxide in a particulate form whose
main ingredient is Li.sub.4Ti.sub.5O.sub.12 contains potassium (K),
wherein (S.sub.SK/S.sub.STi)/(C.sub.k) is 12 or less and preferably
(S.sub.SK/S.sub.STi)-(S.sub.IK/S.sub.ITi) is 0.01 or less, where
S.sub.SK is the K2p peak area of potassium (K) and S.sub.STi is the
Ti2p peak area of titanium (Ti) based on X-ray photoelectron
spectral measurement of the particle surface, C.sub.k is the
content ratio (percent by mass) of potassium (K), S.sub.IK is the
K2p peak area of potassium (K) and S.sub.ITi is the Ti2p peak area
of titanium (Ti) based on X-ray photoelectron spectral measurement
in the interior of the particle. The lithium-titanium complex oxide
is suitable for manufacture of high-capacity batteries.
Inventors: |
KAWAMURA; Chie;
(Takasaki-shi, JP) ; MOCHIGI; Masaki;
(Takasaki-shi, JP) ; ITO; Daigo; (Takasaki-shi,
JP) ; WAGAWA; Akitoshi; (Takasaki-shi, JP) ;
OGATA; Yoichiro; (Takasaki-shi, JP) ; OCHIAI;
Toshiyuki; (Takasaki-shi, JP) ; SUZUKI;
Toshimasa; (Takasaki-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
TAIYO YUDEN CO., LTD.; |
Tokyo |
|
JP |
|
|
Assignee: |
TAIYO YUDEN CO., LTD.
Tokyo
JP
|
Family ID: |
48637974 |
Appl. No.: |
13/688032 |
Filed: |
November 28, 2012 |
Current U.S.
Class: |
252/182.1 |
Current CPC
Class: |
C01G 23/005 20130101;
Y02E 60/10 20130101; C01P 2002/54 20130101; H01M 4/485 20130101;
C01P 2006/12 20130101; H01M 4/131 20130101; C01P 2006/80 20130101;
C01P 2002/32 20130101; C01P 2002/74 20130101; C01P 2002/85
20130101; C01P 2002/52 20130101 |
Class at
Publication: |
252/182.1 |
International
Class: |
H01M 4/485 20060101
H01M004/485 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 26, 2011 |
JP |
2011-284288 |
Claims
1. A lithium-titanium complex oxide in a particulate form whose
main ingredient is Li.sub.4Ti.sub.5O.sub.12 and which contains
potassium (K), wherein (S.sub.SK/S.sub.STi)/(C.sub.k) is 12 or
less, where S.sub.SK is a K2p peak area of potassium (K) and
S.sub.STi is a Ti2p peak area of titanium (Ti) based on X-ray
photoelectron spectral measurement of the particle surface, and
C.sub.k is a content ratio (percent by mass) of potassium (K).
2. A lithium-titanium complex oxide according to claim 1, wherein
(S.sub.SK/S.sub.STi)-(S.sub.IK/S.sub.ITi) is 0.01 or less, where
S.sub.IK is a K2p peak area of potassium (K) and S.sub.m is a Ti2p
peak area of titanium (Ti) based on X-ray photoelectron spectral
measurement on an interior of the particle, and S.sub.SK and
S.sub.STi are defined above.
3. A lithium-titanium complex oxide according to claim 1,
containing 0.01 to 0.25 percent by mass of potassium (K).
4. A lithium-titanium complex oxide according to claim 1, wherein a
mol ratio of lithium to titanium, or Li/Ti, is 0.76 to 0.84.
5. A lithium-titanium complex oxide according to claim 1, further
containing sulfur.
6. A positive electrode for a battery containing the
lithium-titanium complex oxide according to claim 1 as a positive
electrode active material.
7. A negative electrode for a battery containing the
lithium-titanium complex oxide according to claim 1 as a negative
electrode active material.
8. A lithium ion secondary battery having a positive electrode
containing a lithium-titanium complex oxide in a particulate form
whose main ingredient is Li.sub.4Ti.sub.5O.sub.12 and which
contains potassium (K), wherein (S.sub.SK/S.sub.STi)/(C.sub.k) is
12 or less, or a negative electrode containing a lithium-titanium
complex oxide in a particulate form whose main ingredient is
Li.sub.4Ti.sub.5O.sub.12 and which contains potassium (K), wherein
(S.sub.SK/S.sub.STi)/(C.sub.k) is 12 or less, where S.sub.SK is a
K2p peak area of potassium (K) and S.sub.STi is a Ti2p peak area of
titanium (Ti) based on X-ray photoelectron spectral measurement of
the particle surface, and C.sub.k is a content ratio (percent by
mass) of potassium (K).
9. A lithium-titanium complex oxide according to claim 2,
containing 0.01 to 0.25 percent by mass of potassium (K).
10. A lithium-titanium complex oxide according to claim 2, wherein
a mol ratio of lithium to titanium, or Li/Ti, is 0.76 to 0.84.
11. A lithium-titanium complex oxide according to claim 3, wherein
a mol ratio of lithium to titanium, or Li/Ti, is 0.76 to 0.84.
12. A lithium-titanium complex oxide according to claim 2, further
containing sulfur.
13. A lithium-titanium complex oxide according to claim 3, further
containing sulfur.
14. A lithium-titanium complex oxide according to claim 4, further
containing sulfur.
15. A positive electrode for a battery containing the
lithium-titanium complex oxide according to claim 2 as a positive
electrode active material.
16. A positive electrode for a battery containing the
lithium-titanium complex oxide according to claim 3 as a positive
electrode active material.
17. A positive electrode for a battery containing the
lithium-titanium complex oxide according to claim 4 as a positive
electrode active material.
18. A negative electrode for a battery containing the
lithium-titanium complex oxide according to claim 2 as a negative
electrode active material.
19. A negative electrode for a battery containing the
lithium-titanium complex oxide according to claim 3 as a negative
electrode active material.
20. A negative electrode for a battery containing the
lithium-titanium complex oxide according to claim 4 as a negative
electrode active material.
Description
BACKGROUND
[0001] 1. Field of the Invention
[0002] The present invention relates to a lithium ion secondary
battery, an electrode thereof, and a lithium-titanium complex oxide
titanate suitable as the material of such electrode.
[0003] 2. Description of the Related Art
[0004] Lithium titanates having a spinel structure such as
Li.sub.4Ti.sub.5O.sub.12 undergo little volume change and are
highly safe. Lithium ion secondary batteries using these lithium
titanates for their negative electrode are beginning to be used in
automotive and infrastructure applications. However, the market is
demanding significant reduction of battery cost. Carbon materials
are generally used to make negative electrodes and, although their
safety is inferior to lithium titanates, carbon materials offer
high capacity and are much cheaper than lithium titanates.
Accordingly, it is important to maintain the high performance of
lithium titanates and still increase the efficiency of their
manufacturing process. The performances (electrochemical
characteristics) required of lithium titanates include high
capacity, high rate characteristics (high-speed charge/discharge)
and long life.
[0005] Known methods to synthesize lithium titanates include the
wet method and solid phase method. The wet method provides fine
particles of high crystalline property and, among the various types
of wet methods, the sol-gel method allows for uniform solution of
those elements that are otherwise difficult to convert into solid
solution or available only in trace amounts. However, the wet
method as a whole presents many economic and environmental
challenges because the materials used are expensive, processes are
complex, and large amounts of effluent must be treated. The solid
phase method is advantageous in terms of mass production because
the materials used are less expensive and readily available and
processes are simple. Accordingly, it is proposed to use the solid
phase method by adding trace elements to obtain lithium titanate
particles offering good characteristics.
[0006] Patent Literature 1 discloses a lithium titanate as an
active material used for lithium secondary batteries demonstrating
excellent charge/discharge characteristics, wherein such lithium
titanate has a K.sub.2O content of 0.10 to 0.25 percent by mass and
P.sub.2O.sub.5 content of 0.10 to 0.50 percent by mass and is
mainly constituted by Li.sub.4Ti.sub.5O.sub.12. Patent Literature 2
discloses a lithium titanate containing sulfur and also describes
the Li/Ti ratio. Patent Literature 3 discloses that, if unreacted
Li component such as hydroxide, carbonate, or the like that are not
taken into the lithium titanate is exposed at the surface and the
pH value increases to over 11.2 as a result, the battery
performance tends to drop. According to Patent Literature 3,
because this unreacted Li component reacts with a non-aqueous
electrolyte and generates carbon dioxide or hydrocarbon gas, and
also because this secondary reaction causes an organic film to form
on the surface of the active material and become a resistance
component, the battery performance, especially high-temperature
cycle performance and output performance, can be improved by
reducing the unreacted Li component to a pH level of less than
11.2.
BACKGROUND ART LITERATURES
[0007] [Patent Literature 1] Japanese Patent No. 4558229
[0008] [Patent Literature 2] Japanese Patent Laid-open No.
2011-113796
[0009] [Patent Literature 3] Japanese Patent Laid-open No.
2007-18883
SUMMARY
[0010] When an electrode coating solution (electrode paste) is
produced using a lithium-titanium complex oxide containing
potassium (K), problems occur such as the viscosity changing
depending on the lithium-titanium complex oxide used and viscosity
or agglomerated state changing over time. In particular, it has
been shown that the aforementioned problems occur easily when the
potassium (K) concentration at the surface is high. It has also
been shown that the aforementioned problems become prominent when
the Li/Ti mol ratio is high.
[0011] In consideration of the above, the object of the present
invention is to provide a lithium-titanium complex oxide that is
suitable for manufacture of high-capacity batteries, can be
manufactured using the solid phase method associated with low
manufacturing cost, and offers preservation stability, as well as
an electrode and lithium ion secondary battery using such
lithium-titanium complex oxide.
[0012] Any discussion of problems and solutions involved in the
related art has been included in this disclosure solely for the
purposes of providing a context for the present invention, and
should not be taken as an admission that any or all of the
discussion were known at the time the invention was made.
[0013] The inventors of the present invention completed the
invention described below.
[0014] According to the present invention, a lithium-titanium
complex oxide in a particulate form whose main ingredient is
Li.sub.4Ti.sub.5O.sub.12 and which contains potassium (K) is
provided, where (S.sub.SK/S.sub.STi)/(C.sub.k) is 12 or less. Here,
S.sub.SK is the K2p peak area of potassium (K) and S.sub.STi is the
Ti2p peak area of titanium (Ti) based on X-ray photoelectron
spectral measurement of the particle surface, and C.sub.k is the
content ratio (percent by mass) of potassium (K).
[0015] Furthermore, preferably
(S.sub.SK/S.sub.STi)-(S.sub.IK/S.sub.ITi) is 0.01 or less. Here,
S.sub.IK is the K2p peak area of potassium (K) and S.sub.ITi is the
Ti2p peak area of titanium (Ti) based on X-ray photoelectron
spectral measurement on the interior of the particle of the
lithium-titanium complex oxide, and S.sub.SK and S.sub.STi are as
explained above.
[0016] Or, preferably the lithium-titanium complex oxide contains
0.01 to 0.25 percent by mass of potassium (K), while the mol ratio
of lithium to titanium, or Li/Ti, is 0.76 to 0.84 in another
favorable embodiment, and the lithium-titanium complex oxide
contains sulfur in another favorable embodiment.
[0017] According to the present invention, a battery electrode that
contains the aforementioned lithium-titanium complex oxide as an
active material is provided. This electrode may be a positive
electrode or negative electrode. Furthermore, according to the
present invention, a lithium ion secondary battery having such
positive electrode or negative electrode is provided.
[0018] The lithium-titanium complex oxide proposed by the present
invention contains potassium (K) and is suitable for manufacture of
high-capacity lithium ion secondary batteries. Also, a paste
containing this lithium-titanium complex oxide offers excellent
stability over time because adsorption of CO.sub.2 and water is
suppressed due to a low abundance ratio of potassium at the
material surface. In a favorable embodiment, potassium is contained
in a relatively uniform manner in the depth direction of the
lithium-titanium complex oxide, which prominently increases the
battery capacity and improves paste stability over time as
mentioned above. When adsorption of CO.sub.2 and water is
suppressed, as mentioned above, the stability over time of a paste
containing this lithium-titanium complex oxide improves and a
smooth electrode sheet can be produced continuously, which in turn
improves the manufacturing efficiency and also prevents the
electrolyte solution and electrode from reacting to each other when
a lithium ion secondary battery is manufactured, thereby achieving
the improved cycle characteristics of the battery as mentioned
above.
[0019] For purposes of summarizing aspects of the invention and the
advantages achieved over the related art, certain objects and
advantages of the invention are described in this disclosure. Of
course, it is to be understood that not necessarily all such
objects or advantages may be achieved in accordance with any
particular embodiment of the invention. Thus, for example, those
skilled in the art will recognize that the invention may be
embodied or carried out in a manner that achieves or optimizes one
advantage or group of advantages as taught herein without
necessarily achieving other objects or advantages as may be taught
or suggested herein.
[0020] Further aspects, features and advantages of this invention
will become apparent from the detailed description which
follows.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] These and other features of this invention will now be
described with reference to the drawings of preferred embodiments
which are intended to illustrate and not to limit the invention.
The drawings are greatly simplified for illustrative purposes and
are not necessarily to scale.
[0022] FIG. 1 is a schematic section view of a half cell.
[0023] FIG. 2 is a schematic section view of a full cell.
DESCRIPTION OF THE SYMBOLS
[0024] 1 Al lead
[0025] 2 Thermo-compression bonding tape
[0026] 3 Kapton tape
[0027] 4 Aluminum foil
[0028] 5, 15, 16 Electrode mixture
[0029] 6 Metal Li plate
[0030] 7 Ni mesh
[0031] 8 Ni lead
[0032] 9 Separator
[0033] 10 Aluminum laminate
DETAILED DESCRIPTION OF EMBODIMENTS
[0034] The ceramic material proposed by the present invention is
mainly constituted by a lithium-titanium complex oxide of spinel
structure expressed by Li.sub.4Ti.sub.5O.sub.12, where this
lithium-titanium complex oxide typically accounts for 90% or more,
or preferably 95% or more, of the ceramic material proposed by the
present invention. In this Specification, such ceramic material is
referred to as "lithium-titanium complex oxide."
[0035] According to the present invention, the lithium-titanium
complex oxide is a particulate, where the particle may be in a
powder form where very small particles are aggregated together, or
an inorganic component contained in a paste into which a resin
(binder) has been mixed, or a molding obtained by heat-treating
such paste, for example.
[0036] Potassium is a required trace constituent that must be
contained in the lithium-titanium complex oxide. The content of
potassium (equivalent K atom content) is preferably 0.01 to 0.25
percent by mass, or more preferably 0.05 to 0.2 percent by mass,
based on the mass of the lithium-titanium complex oxide being 100%.
The lithium-titanium complex oxide may contain sulfur, where the
content of sulfur (equivalent S atom content) is preferably 0.01 to
0.09 percent by mass. The lithium-titanium complex oxide may
contain phosphorous, where the content of phosphorous (equivalent P
atom content) is preferably 0.013 to 0.24 percent by mass, or more
preferably 0.05 to 0.2 percent by mass. Presence of potassium
allows a lithium-titanium complex oxide of higher initial discharge
capacity to be obtained, where coexistence of phosphorous makes
this effect more prominent. In a favorable embodiment of the
present invention, the lithium-titanium complex oxide contains
sulfur and consequently adsorption of carbon dioxide and water is
more prominently suppressed and preservation stability of a paste,
etc., containing the lithium-titanium complex oxide improves.
[0037] According to the present invention, the main crystalline
system of the lithium-titanium complex oxide is a lithium titanate
of spinel structure, which is expressed by the composition formula
of Li.sub.4Ti.sub.5O.sub.12 and can be confirmed by the presence of
a specified X-ray diffraction peak. The lithium-titanium complex
oxide may have intermediate phases such as TiO.sub.2 and
Li.sub.2TiO.sub.3 mixed in it, where these intermediate phases
cause the charge/discharge capacity of the battery to drop. Lower
abundance of Li.sub.2TiO.sub.3 is preferable because water and
CO.sub.2 will not be absorbed easily. Lower abundance of secondary
phases and intermediate layers means the mol ratio of lithium to
titanium (Li/Ti) in the lithium-titanium complex oxide is close to
the stoichiometric composition, or 4/5 to be specific, and in this
sense the aforementioned mol ratio is preferably 0.76 to 0.84.
[0038] Under the solid phase method, the lithium-titanium complex
oxide is typically obtained by mixing and sintering a titanium
compound, lithium compound, and trace constituents. For the source
titanium, a titanium oxide is typically used. The particle size of
the lithium-titanium complex oxide is affected by the particle size
of titanium oxide. Accordingly, use of a fine titanium oxide tends
to easily produce a fine lithium-titanium complex oxide. On the
other hand, preferably the specific surface area of the titanium
oxide is in a range of 8 to 30 m.sup.2/g in order to avoid
cohesion, which in turn will require more energy for mixing. For
the source lithium, a carbonate, acetate or hydroxide is typically
used. If a lithium hydroxide is used, it may be a hydrate such as
monohydrate or the like. For the source lithium, two or more of the
foregoing may be combined. Preferably a source lithium is mixed
while being crushed and made finer to a maximum particle size of 10
.mu.m or less, or a source lithium having a small maximum particle
size is used from the beginning, as it would lower the
lithium-titanium complex oxide production temperature, which is
favorable when manufacturing a fine lithium-titanium complex oxide.
It should be noted that, since lithium may decrease as a result of
partial volatilization, loss due to sticking to equipment walls, or
for other reasons in the manufacturing process, it is preferable to
use a greater amount of source lithium than the final target amount
of Li.
[0039] It should be noted that, as mentioned above, Li may decrease
as a result of volatilization, loss due to sticking to equipment
walls, or for other reasons, during the manufacturing process. The
ratio of source lithium and source titanium used as the materials
should be determined by considering this decrease in Li. To get an
idea on the level of decrease in Li, the results of examples
explained later can be used as reference. These data can be used to
easily determine the amount of source lithium to be added.
[0040] According to the present invention, the obtained
lithium-titanium complex oxide may contain potassium of a specified
ratio amount, and it may further contain sulfur or phosphorous.
These elements can be added to the materials in the form of oxides
of potassium, phosphorous and sulfur, respectively, or in the form
of potassium, phosphorous and sulfur with other compounds (for
example, compounds with lithium and titanium).
[0041] For the source potassium, a carbonate, hydrogen carbonate,
or hydroxide etc is typically used.
[0042] For the source phosphorous, an ammonium phosphate, etc., can
be used. By using a potassium dihydrogen phosphate, dipotassium
hydrogenphosphate, tripotassium phosphate or other substance
containing both potassium and phosphorous, the source potassium and
source lithium can be satisfied by only one compound.
[0043] For the source sulfur, any alkali metal salt of sulfur,
especially lithium sulfate or potassium sulfate, is typically used.
Lithium sulfate and potassium sulfate can be used not only as a
source sulfur, but also as a source lithium or source
potassium.
[0044] The lithium-titanium complex oxide proposed by the present
invention may contain only each of the elements mentioned above, or
it may further contain, in addition to the foregoing elements,
trace amounts of silicon, zirconium, niobium, calcium, sodium,
etc.
[0045] According to the present invention, preferably little
potassium is present at the surface of the lithium-titanium complex
oxide particle. Presence of potassium at the particle surface can
be measured using an X-ray photoelectron spectrum. To be specific,
X-ray photoelectron spectral measurement is performed on the
surface of the particle of the particulate lithium-titanium complex
oxide to be measured, to obtain the K2p peak area of potassium (K)
as S.sub.SK. Similarly, X-ray photoelectron spectral measurement is
performed on the particle surface to calculate the Ti2p peak area
of titanium (Ti) as S.sub.STi. The content ratio of potassium (K)
in the lithium-titanium complex oxide is given as (C.sub.k)
(percent by mass). Equation (1) below using these values should
yield a value of 12 or less:
(S.sub.SK/S.sub.STi)/(C.sub.K) Equation (1)
[0046] This shows that a lower abundance of potassium at the
surface allows less water and CO.sub.2 to be adsorbed and
consequently the preservation stability of a paste, etc.,
containing this lithium-titanium complex oxide improves.
[0047] Preferably the potassium concentration is almost constant
over a specified range from the surface of the lithium-titanium
complex oxide. In other words, preferably the abundance of
potassium at the surface of the particle of the lithium-titanium
complex oxide is equivalent to the abundance of potassium on the
interior of the particle. Presence of potassium in the particle can
also be measured using an X-ray photoelectron spectrum. To be
specific, X-ray photoelectron spectral measurement is performed on
the interior of the particle of the particulate lithium-titanium
complex oxide to be measured, to obtain the K2p peak area of
potassium (K) as S.sub.IK. Similarly, X-ray photoelectron spectral
measurement is performed on the interior of the particle to
calculate the Ti2p peak area of titanium (Ti) as S.sub.ITi.
Equation (2) below using these measured values as well as S.sub.IK
and S.sub.ITi explained above should yield a value of 0.01 or
less:
(S.sub.SK/S.sub.STi)-(S.sub.IK/S.sub.ITi) Equation (2)
[0048] Here, measurement on the interior of the particle is
performed by subjecting the lithium-titanium complex oxide particle
to Ar ion sputtering under the same conditions that achieve
sputtering to a depth of 40 nm in the case of a SiO.sub.2 film,
after which X-ray photoelectron spectral measurement is
performed.
[0049] According to the present invention, required potassium is
present evenly in the lithium-titanium complex oxide. Accordingly,
a high-capacity battery is obtained and, because there is less
potassium at the surface, amounts of water and CO.sub.2 absorbed
are suppressed. Preferably the specific surface area of the
lithium-titanium complex oxide is 3 to 14 m.sup.2/g.
[0050] According to the present invention, a high-quality
lithium-titanium complex oxide can be obtained using the solid
phase method. Under the solid phase method, the aforementioned
materials are weighed and then mixed and sintered. In the mixing
process, simultaneously adding a crushing effect reduces the growth
of lithium-titanium complex oxide particles because the thermal
decomposition reaction temperature of lithium carbonate as
described later decreases. The mixing process may be wet mixing or
dry mixing. Wet mixing is a method whereby a dispersion medium such
as water, ethanol or the like is used together with a ball mill,
planetary ball mill, bead mill, wet jet mill, etc. Dry mixing is a
method where a ball mill, planetary ball mill, bead mill, vertical
type roller mill, jet mill or flow-type mixer, an air stream style
grinder such as cyclone mill, or machines capable of applying
compressive force or shearing force to achieve precision mixing or
efficiently add mechano-chemical effect such as Nobilta (Hosokawa
Micron) and Miralo (Nara Machinery), etc., or two or more of the
foregoing combined, is/are used for mixing without using dispersion
medium.
[0051] In the case of dry mixing, water or organic solvent can be
used as a mixing auxiliary. For the organic solvent, alcohol,
ketone, etc., can be used. Examples of the alcohol include
methanol, ethanol, propanol, butanol, ethylene glycol, propylene
glycol, diethylene glycol, triethylene glycol, dipropylene glycol,
tripropylene glycol, glycerin, and the like, while examples of the
ketone include acetone, diethyl ketone, methyl ethyl ketone, methyl
isobutyl ketone, acetyl acetone, cyclohexanone, and the like. Any
one of the foregoing or mixture of two or more can be added by a
trace amount to increase the efficiency of mixing.
[0052] In the case of wet mixing, load in the drying process can be
reduced by minimizing the use of the dispersion medium. If the
amount of dispersion medium is too little, the slurry becomes
highly viscous and may clog the piping or present other problems.
Accordingly, preferably a small amount (approx. 5 percent by mass
or less) of dispersion medium such as polyacrylate or the like is
used, where desirably the solid content is adjusted to a range of
4.8 to 6.5 mol/L for Li material and 6 to 7.9 mol/L for titanium
oxide at the time of mixing.
[0053] At the time of mixing, the order in which the dispersion
medium (water, etc.), dispersant, Li material and titanium material
are added does not affect the quality of the final product. For
example, the dispersion medium, dispersant, Li material and
titanium material can be added, in this order, under agitation
using agitating blades. Or, the Li material and titanium material
can be roughly mixed beforehand and then added in the last step, as
it saves mixing time and increases efficiency.
[0054] Whichever mixing method is used, if a carbonate is used for
the source Li, it is preferable to mix the ingredients until the
weight loss due to CO.sub.2 dissociation caused by breakdown of
lithium carbonate no longer occurs based on heat analysis
measurement of the material mixed powder at 700.degree. C. or
below. In this case, the measurement conditions for heat analysis
are as follows: Use a platinum container of 5 mm in diameter, 5 mm
in height and 0.1 mm in thickness, 15 mg of sample and
Al.sub.2O.sub.3 as a standard sample; raise the temperature at a
rate of 5.degree. C./min up to 850.degree. C.; and introduce, as an
ambient gas, a gas mixture consisting of 80% nitrogen and 20%
oxygen, by the flow rate recommended for the heat analyzer. Any
measurement system can be used, such as Thermo Plus TG8120 by
Rigaku or TG-DTA2000S by Mac Science and the like, as these
machines achieve similar results. If breakdown of lithium carbonate
does not end at 700.degree. C. or below, mixing should be continued
until the thermal breakdown temperature becomes 700.degree. C. or
below. It is deemed that the lower the ending temperature of
thermal breakdown of lithium carbonate, the more uniformly the
source titanium and lithium carbonate are mixed, which in turn
allows for a lower setting of sintering temperature and reduces the
growth of lithium-titanium complex oxide particles. In addition, by
mixing the ingredients until the thermal breakdown temperature of
lithium carbonate becomes 700.degree. C. or below, mixing of the
trace amounts of potassium compound, phosphorous compound, and
niobium compound added will progress sufficiently.
[0055] For the sintering temperature after mixing, a typical
condition is 700 to 1000.degree. C., and a preferable condition is
700 to 900.degree. C. The sintering time is preferably 12 hours or
less, or more preferably 5 hours or less.
[0056] The amount of the lithium-titanium complex oxide of spinel
structure expressed by Li.sub.4Ti.sub.5O.sub.12, contained in the
lithium-titanium complex oxide proposed by the present invention,
can be obtained by powder X-ray diffraction measurement. Powder
X-ray diffraction measurement was performed by powder XRD (Ultima
IV by Rigaku, target Cu, acceleration voltage 40 kV, discharge
current 40 mA, divergence slit width 1.degree., divergence
longitudinal slit width 10 mm). The peak intensity ratio of each
compound is expressed relative to the peak intensity on the
Li.sub.4Ti.sub.5O.sub.12 (111) plane (2.theta.=18.331) being 100.
The value of each 2.theta. was taken from the JCPDS card.
[0057] The peak intensity ratio of the Li.sub.4Ti.sub.5O.sub.12
(111) plane is calculated as follows:
[0058] Peak intensity ratio of Li.sub.4Ti.sub.5O.sub.12 (111)
plane=a/(a+b+c+d+e).times.100
[0059] (a: Peak intensity of Li.sub.4Ti.sub.5O.sub.12 (111) plane
(2.theta.=18.331), b: Peak intensity of Li.sub.2TiO.sub.3 (-133)
plane (2.theta.=48.583), c: Peak intensity of rutile TiO.sub.2
(110) plane (2.theta.=27.447), d: Peak intensity of
KTi.sub.8O.sub.16 (310) plane (2.theta.=27.610), e: Main peak
intensity of a compound derived from other trace element
[0060] By adjusting the peak intensity ratio of the
Li.sub.4Ti.sub.5O.sub.12 (111) plane to 90% or greater, or
preferably 95% or greater, the initial discharge capacity can be
increased. Preferably the sintering temperature and sintering time
are adjusted as deemed appropriate so that the specific surface
area becomes 3 to 11 m.sup.2/g, and by adjusting the specific
surface area to this range, the secondary battery will express high
rate characteristics.
[0061] There is no limitation on the sintering ambience, and
sintering can be performed in atmosphere, oxygen atmosphere, or
inert gas atmosphere, under either atmospheric pressure or
decompression. Sintering can also be performed multiple times.
Sintered powder may be crushed/classified or re-sintered, as
necessary. Although the solid phase method discussed above is
advantageous in terms of cost among the manufacturing methods for
lithium-titanium complex oxide, the sol-gel method or wet method
using alkoxide can also be adopted.
[0062] One way to cause less potassium to be present at the surface
of the lithium-titanium complex oxide, and roughly uniformly
throughout the lithium-titanium complex oxide, is to crush the
powder after the aforementioned sintering. Crushing can be
implemented by the material mixing method described above. If water
is used as a dispersant to perform wet crushing, the dispersant can
be filtered or solid contents separated by sedimentation to remove
the dispersant, in order to reduce the potassium concentration at
the surface. The remaining amount of potassium can be controlled by
means of controlling the ratio of remaining water in the cake.
Crushing can also be performed after drying the cake.
[0063] Next, preferably heat treatment is performed again
(annealing). Favorable annealing conditions include 100 to
600.degree. C. for 1 minute to 3 hours. To be more specific,
preferably annealing is performed by (A) keeping the maximum
annealing temperature to 490.degree. C. or below or (B) keeping the
maximum annealing temperature to within 490 and 600.degree. C. and
also adjusting the ambient CO.sub.2 to 10 ppm or less and water to
50.degree. C. below the dew point in the subsequent cooling to room
temperature.
[0064] Condition (A) above prevents a liquid phase with potassium
and lithium from generating easily, while condition (B) above makes
adsorption of CO.sub.2 and water more difficult, thereby ensuring
excellent stability over time of a paste containing the obtained
lithium-titanium complex oxide.
[0065] Annealing can be performed under decompression or
atmospheric pressure, or in an atmosphere containing oxygen or
inert atmosphere, and if an organic substance is added during
crushing, an atmosphere containing oxygen is suitable.
[0066] The lithium-titanium complex oxide proposed by the present
invention can be used favorably as an active electrode material for
lithium ion secondary batteries. It can be used for positive
electrodes or negative electrodes. The configurations and
manufacturing methods of electrodes containing the lithium-titanium
complex oxides, their active material, and lithium ion secondary
battery having such electrodes, can apply any prior technology as
deemed appropriate.
[0067] Also in the examples explained later, an example of
manufacturing a lithium ion secondary battery is presented.
Typically a suspension agent containing the lithium-titanium
complex oxide as an active material, conductive auxiliary, binder,
and appropriate solvent is prepared and this suspension agent is
applied to the metal piece of the current collector, etc., and
dried, and then pressed to form an electrode.
[0068] For the conductive auxiliary, metal powder such as carbon
material, aluminum powder or the like, or conductive ceramics such
as TiO or the like can be used. Examples of the carbon material
include acetylene black, carbon black, coke, carbon fiber, and
graphite.
[0069] Examples of the binder include various resins, or
specifically fluororesins etc, for example, polytetrafluoroethylene
(PTFE), polyvinylidene difluoride (PVdF), fluororubber, styrene
butadiene rubber, and the like.
[0070] Preferably the blending ratio of negative electrode active
material, conductive agent, and binder is 80 to 98 percent by mass
of negative electrode active material, 0 to 20 percent by mass of
conductive agent, and 2 to 7 percent by mass of binder.
[0071] The current collector is preferably an aluminum foil or
aluminum alloy foil of 20 .mu.m or less in thickness.
[0072] When the lithium-titanium complex oxide material is used as
a negative electrode active material, the material used for the
positive electrode is not specifically limited and any known
material can be used, where examples include lithium-manganese
complex oxide, lithium-nickel complex oxide, lithium-cobalt complex
oxide, lithium-nickel-cobalt complex oxide,
lithium-manganese-nickel complex oxide, spinel
lithium-manganese-nickel complex oxide, lithium-manganese-cobalt
complex oxide, and lithium iron phosphate, etc.
[0073] For the conductive agent, binder, and current collector for
the positive electrode, those materials mentioned above can be
used. Preferably the blending ratio of positive electrode active
material, conductive agent, and binder is 80 to 95 percent by mass
of positive electrode active material, 3 to 20 percent by mass of
conductive agent, and 2 to 7 percent by mass of binder.
[0074] From the positive/negative electrodes thus obtained, an
electrolyte solution constituted by lithium salt, and an organic
solvent or organic solid electrolyte or inorganic solid
electrolyte, and a separator, etc., a lithium ion secondary battery
can be constituted.
[0075] Examples of the lithium salt include lithium perchlorate
(LiClO.sub.4), lithium hexafluorophosphate (LiPF.sub.6), lithium
tetrafluoroborate (LiBF.sub.4), lithium hexafluoroarsenate
(LiAsF.sub.6), lithium trifluorometanesulfonate
(LiCF.sub.3SO.sub.3), lithium bis-trifluoromethyl sulfonyl imide
[LiN(CF.sub.3SO.sub.2).sub.2], and the like. One type of lithium
salt may be used, or two or more types may be combined. Examples of
the organic solvent include propylene carbonate (PC), ethylene
carbonate (EC), vinylene carbonate and other cyclic carbonates;
diethyl carbonate (DEC), dimethyl carbonate (DMC), methyl ethyl
carbonate (MEC) and other chained carbonates; tetrahydrofuran
(THF), 2-methyl tetrahydrofuran (2MeTHF), dioxolane (DOX) and other
cyclic ethers; dimethoxy ethane (DME), dietoethan (DEE) and other
chained ethers; y-butyrolactone (GBL); acetonitrile (AN); and
sulfolane (SL), etc., either used alone or combined into a mixed
solvent.
[0076] For the organic solid electrolyte, for example, polyethylene
derivative, polyethylene oxide derivative or polymer compound
containing it, or polypropylene oxide derivative or polymer
compound containing it, is suitable. Among the inorganic solid
electrolytes, Li nitride, halogenated Li, and Li oxyate are
well-known. In particular, Li.sub.4SiO.sub.4,
Li.sub.4SiO.sub.4--LiI--LiOH,
xLi.sub.3PO.sub.4-(1-x)Li.sub.4SiO.sub.4, Li.sub.2SiS.sub.3,
Li.sub.3PO.sub.4--Li.sub.2S--SiS.sub.2, phosphorus sulfide
compound, etc., are effective.
[0077] For the separator, a polyethylene microporous membrane is
used. The separator is installed between the two electrodes in a
manner not allowing the positive electrode and negative electrode
to contact each other.
EXAMPLES
[0078] The present invention is explained more specifically using
examples. It should be noted, however, that the present invention
is not limited to the embodiments described in these examples.
First, how the samples obtained by the examples/comparative
examples were analyzed and evaluated is explained.
[0079] (Element Analysis)
[0080] Samples of lithium-titanium complex oxide were put through
pressurized acid decomposition, after which atomic absorption
spectrometry or ICP atomic emission spectroscopy measurement was
used to perform quantitative analysis of the contained elements.
The abundance ratios (percent by mass) of potassium, phosphorous
and sulfur were calculated based on the weight of the
lithium-titanium complex oxide being 100%. For lithium, the value
quantified by ICP atomic emission spectroscopy was used. For
titanium, the value obtained as the difference between the amount
of ignition loss at up to 900.degree. C. and mass of all elements
quantified by the element analysis was used, and the Li/Ti mol
ratio was calculated accordingly.
[0081] (Battery Evaluation--Half Cell)
[0082] FIG. 1 is a schematic section view of a half cell. With this
cell, lithium metal is used for the counter electrode, so the
potential of the electrode shown is nobler than that of the counter
electrode. Accordingly, the directions of charge/discharge are the
opposite of those applicable when lithium-titanium complex oxide is
used for the negative electrode.
[0083] To avoid confusion, the direction in which lithium ions are
inserted into the lithium-titanium complex oxide electrode is
called "charge," while the direction in which lithium ions
dissociate from the electrode is called "discharge." An electrode
mixture was prepared using lithium-titanium complex oxide as an
active material. Ninety parts by weight of the obtained
lithium-titanium complex oxide as an active material, 5 parts by
weight of acetylene black as a conductive auxiliary, and 5 parts by
weight of fluororesin as a binder, were mixed using
n-methyl-2-pyrrolidon as a solvent.
[0084] This electrode mixture 5 was applied to an aluminum foil 4
to a coating weight of 0.003 g/cm.sup.2 using the doctor blade
method. The coated foil was vacuum-dried at 130.degree. C., and
then roll-pressed. Thereafter, an area of 10 cm.sup.2 was stamped
out from the pressed foil to obtain a working electrode of a
battery. For the counter electrode, a metal Li plate 6 attached to
a Ni mesh 7 was used. For the electrolyte solution, ethylene
carbonate and diethyl carbonate were mixed at a volume ratio of
1:2, and then 1 mol/L of LiPF.sub.6 was dissolved into the obtained
solvent. For a separator 9, a porous cellulose membrane was used.
Also, as illustrated, Al leads 1, 8 were fixed using a
thermo-compression bonding tape 2, and the Al lead 1 was fixed to
the working electrode using a Kapton tape 3. An aluminum laminate
cell 10 was thus prepared. This battery was used to measure the
initial discharge capacity. The battery was charged to 1.0 V at a
constant current of 0.105 mA/cm.sup.2 (0.2 C) in current density,
and then discharged to 3.0 V, with the cycle repeated three times
and the discharge capacity in the third cycle used as the value of
initial discharge capacity. Preferably the initial discharge
capacity is 155 mAh/g or more. Next, the rate characteristics were
measured. The battery was charged to 1.0 V at a constant current of
0.525 mA/cm.sup.2 in current density, and then discharged to 3.0 V,
with the cycle repeated twice and similar measurements performed by
increasing the current density in steps to 1.05 mA/cm.sup.2, 1.575
mA/cm.sup.2, 2.626 mA/cm.sup.2, 5.25 mA/cm.sup.2, and 8
mA/cm.sup.2. The ratio of the discharge capacity in the second
cycle at a current density of 8 mA/cm.sup.2, and the value of
initial discharge capacity, was indicated as the rate
characteristics (%). Preferably the rate characteristics are 60% or
more.
[0085] (Battery Evaluation--Full Cell)
[0086] FIG. 2 is a schematic section view of a full cell. A
negative electrode mixture 15 was prepared using as an active
material the lithium-titanium complex oxide obtained in Example 1
mentioned later. To be specific, a negative electrode using the
obtained lithium-titanium complex oxide as its active material was
manufactured in the same manner as the working electrode of the
half cell mentioned above. A positive electrode mixture 16 was
obtained by mixing 90 parts by weight of lithium cobaltate as an
active material (D50%=10 .mu.m), 5 parts by weight of acetylene
black as a conductive auxiliary, and 5 parts by weight of
fluororesin as a binder, together with n-methyl-2-pyrrolidone as a
solvent. This electrode mixture was applied to an aluminum foil to
a coating weight of 0.0042 g/cm.sup.2 using the doctor blade
method. The coated foil was vacuum-dried at 130.degree. C., and
then roll-pressed to obtain a positive electrode. The electrolyte
solution and separator 9 conformed to those of the half cell
mentioned above. An aluminum laminate cell was thus prepared. This
battery was used to measure the initial discharge capacity. The
battery was charged to 2.8 V at a constant current of 0.105
mA/cm.sup.2 (0.2 C) in current density, and then discharged to 1.5
V, with the cycle repeated three times and the discharge capacity
in the third cycle used as the value of initial discharge capacity.
Next, the rate characteristics were measured. The battery was
charged to 1.5 V at a constant current of 0.525 mA/cm.sup.2 in
current density, and then discharged to 2.8 V, with the cycle
repeated twice and similar measurements performed by increasing the
current density in steps to 1.05 mA/cm.sup.2, 1.575 mA/cm.sup.2,
2.625 mA/cm.sup.2, 5.25 mA/cm.sup.2, and 8 mA/cm.sup.2. The ratio
of the discharge capacity in the second cycle at a current density
of 8 mA/cm.sup.2, and the value of initial discharge capacity, was
indicated as the rate characteristics (%).
[0087] (XPS Measurement)
[0088] Preparation of sample: 25 mg of powder sample was put in a
6.5-mm diameter aluminum container for thermal analysis and pressed
with a single-axis pressurization hydraulic press at a pressure of
30 kgf/cm.sup.2 for 1 minute, after which the pressed powder was
let stand overnight in an XPS measurement apparatus and then
deaerated in vacuum.
[0089] Measurement: The Quantera SXM by Ulvac-Phi was used. A
monochromatized Al K.alpha. ray (25 W, 15 kV) was used as the
excitation X-ray, with the analysis diameter set to 100 .mu.m and
charge neutralization performed using electrons and Ar ions. The
sample was set horizontally and narrow scan measurement (pass
energy 112 eV, step size 0.1 eV, detector angle 45 degrees) was
performed on Ti2p and K2p to analyze the surface. For the depth
analysis, the sample was set horizontally and the lithium-titanium
complex oxide was subjected to Ar ion sputtering under the same
conditions that would achieve sputtering to a depth of 40 nm for a
SiO.sub.2 film using a standard sample from Ulvac-Phi (25 nm,
SIO.sub.2/Si) at a speed of 1.18 nm/min (area of 2 mm.times.2 mm),
and spectral measurement of K2p and Ti2p was performed at a pass
energy of 112 eV, step size of 0.1 eV and detector angle of 45
degrees. When the KRATOS AXIS-HS by Shimadzu was used (analysis
diameter was set in a range of 500 to 1000 .mu.m during
measurement) with a Mg K.alpha. ray and monochromatized Al K.alpha.
ray at a SiO.sub.2-film sputtering speed of 0.75 nm/min, similar
measured results were obtained. This confirms that measured data
was not dependent on the apparatus.
[0090] (Measurement of CO.sub.2 Amount)
[0091] A GCMS equipped with a thermal decomposition apparatus
(Double-shot Pyrolyzer PY2020iD by Frontier Laboratories) (GC unit:
Agilent 6890, MS unit: Auto Mass AMII) was used. The measurement
sample was introduced into the thermal decomposition unit and let
stand for 3 minutes under a He flow. Thereafter, measurement was
performed at the rate of temperature rise of 20.degree. C./min,
temperature range of 60.degree. C. to 800.degree. C., carrier gas
of He, split ratio of approx. 1/10, column inner diameter and
length of 0.25 mm and 8.7 m (empty column), respectively, GC oven
temperature of 250.degree. C., inlet temperature of 300.degree. C.,
detector of MS, and sample amount of 3 mg. The CO.sub.2 (m/z=44)
area was obtained from the start to end of measurement. Following
the measurement of the measurement sample, 1 mg of calcium oxalate
(CaC.sub.2O.sub.4--H.sub.2O) was measured in the same manner and
the measured results obtained were used to correct the CO.sub.2
area to mass. The measurement sample was measured three times and
an average of three measurements was used as the amount of CO.sub.2
generation. Preferably the amount of CO.sub.2 generation is less
than 3000 ppm by weight in order to ensure paste stability,
etc.
[0092] (Paste Stability over Time)
[0093] An electrode mixture paste containing a lithium-titanium
complex oxide was evaluated for stability over time. For the
electrode mixture paste, the aforementioned paste prepared for the
production of a half cell was used. Using a rheometer (AR-2000) by
TA Instruments, the target paste was measured for viscosity (Pa-s)
at a sheer speed of 1 (1/s) immediately after its production and
after having been let stand for 5 hours, and the difference was
obtained. The paste is considered stable and will not affect the
production efficiency if its viscosity difference is 40 or less in
absolute value.
Example 1
[0094] The ratio of input Li/Ti atoms was set to 0.805. Lithium
carbonate (commercial high-purity reagent of 99% in purity) was
used as a source Li, and a high-purity titanium oxide of 99.9% in
purity and 10.+-.1 m.sup.2/g in specific surface area was used. For
the pure water used as a dispersant, an amount that would give a
concentration of solid contents of 52 percent by mass was added,
while potassium hydroxide was added as a source potassium and
ammonium dihydrogen phosphate, as a source phosphorous, to obtain a
slurry.
[0095] The obtained slurry was mixed under agitation using a bead
mill. Thereafter, the dispersant was removed using a spray dryer
and the remainder was heat-treated in atmosphere at 820.degree. C.
for 3 hours. This was followed by crushing using pure water and a
bead mill, and the filter-pressed cake was dried, and dry-cracked,
and then heat-treated at 500.degree. C. for 1 hour in an ambience
of a mixed gas of 20% 0.sub.2 and 80% N.sub.2 not containing
CO.sub.2 (less than 1 ppm) (dew point--70.degree. C.), after which
the cake was cooled to room temperature without being exposed to
atmosphere.
[0096] The lithium-titanium complex oxide obtained in Example 1 was
also given a full-cell evaluation in addition to the half-cell
evaluation described above. The half-cell evaluation was the same
as shown in Table 1, and the full-cell evaluation results were
exactly the same as the half-cell evaluation results. The value
calculated by Equation (2) above was 0.0008.
Example 2
[0097] The ratio of input Li/Ti atoms was set to 0.805. Lithium
carbonate (commercial high-purity reagent of 99% in purity) was
used as a source Li, and a high-purity titanium oxide of 99.9% in
purity and 10.+-.1 m.sup.2/g in specific surface area was used.
Potassium hydroxide was added as a source potassium and ammonium
dihydrogen phosphate, as a source phosphorous. ZrO.sub.2 balls of
10 in diameter were used to dry-mix the ingredients for 2 hours in
a planetary ball mill, after which the mixture was heat-treated in
atmosphere at 820.degree. C. for 3 hours. This was followed by
crushing using pure water and a bead mill, and the filter-pressed
cake was dried, and dry-cracked, and then heat-treated at
400.degree. C. for 1 hour in an atmosphere of a mixed gas of 20%
0.sub.2 and 80% N.sub.2 not containing CO.sub.2 (less than 1 ppm)
(dew point--70.degree. C.), after which the cake was cooled to room
temperature without being exposed to atmosphere. The value
calculated by Equation (2) above was 0.0010.
Example 3
[0098] A lithium-titanium complex oxide was obtained in the same
manner as in Example 2, except that the amount of the source
potassium was changed and annealing temperature was also changed to
600.degree. C. The value calculated by Equation (2) above was
0.0066.
Example 4
[0099] A lithium-titanium complex oxide was obtained in the same
manner as in Example 2, except that the amount of the source
potassium was changed and annealing temperature was also changed to
500.degree. C. The value calculated by Equation (2) above was
0.0023.
Example 5
[0100] A lithium-titanium complex oxide was obtained in the same
manner as in Example 2, except that the amount of the source
potassium was changed and annealing temperature was also changed to
600.degree. C. The value calculated by Equation (2) above was
0.0100.
Comparative Example 1
[0101] A lithium-titanium complex oxide was obtained in the same
manner as in Example 1, except that potassium hydroxide was not
added.
Comparative Example 2
[0102] A lithium-titanium complex oxide was obtained in the same
manner as in Example 3, except that annealing was performed in the
form of heat-treating at 600.degree. C. for 1 hour under a flow of
air of 25.degree. C. and relative humidity of 90%. The value
calculated by Equation (2) above was 0.0220.
Comparative Example 3
[0103] A lithium-titanium complex oxide was obtained in the same
manner as in Comparative Example 2, except that the amount of the
source potassium was changed.
Example 6
[0104] A lithium-titanium complex oxide was obtained in the same
manner as in Example 1, except that the ratio of input Li/Ti atoms
was changed to 0.764. The value calculated by Equation (2) above
was 0.0007.
Example 7
[0105] A lithium-titanium complex oxide was obtained in the same
manner as in Example 2, except that the amount of the source
potassium was changed and the ratio of input Li/Ti atoms was also
changed to 0.764. The value calculated by Equation (2) above was
0.0050.
Example 8
[0106] A lithium-titanium complex oxide was obtained in the same
manner as in Example 5, except that the ratio of input Li/Ti atoms
was changed to 0.764. The value calculated by Equation (2) above
was 0.0090.
Example 9
[0107] A lithium-titanium complex oxide was obtained in the same
manner as in Example 1, except that the ratio of input Li/Ti atoms
was changed to 0.845. The value calculated by Equation (2) above
was 0.0007.
Example 10
[0108] A lithium-titanium complex oxide was obtained in the same
manner as in Example 7, except that the ratio of input Li/Ti atoms
was changed to 0.845. The value calculated by Equation (2) above
was 0.0020.
Example 11
[0109] A lithium-titanium complex oxide was obtained in the same
manner as in Example 5, except that the ratio of input Li/Ti atoms
was changed to 0.845. The value calculated by Equation (2) above
was 0.0020.
Examples 12, 13
[0110] A lithium-titanium complex oxide was obtained in the same
manner as in Example 7, except that the ratio of input Li/Ti atoms
was changed to 0.805 and lithium sulfate was added further as a
material. The amount of sulfur is shown in Table 1. The value
calculated by Equation (2) above was 0.0070 (Example 12) and 0.0060
(Example 13).
Examples 14 to 17
[0111] A lithium-titanium complex oxide was obtained in the same
manner as in Example 7, except that the amount of phosphorous was
changed according to Table 1. The value calculated by Equation (2)
above was 0.0070 (Example 14), 0.0080 (Example 15), 0.0080 (Example
16), and 0.0080 (Example 17).
[0112] The compositions and measured results/evaluation results of
obtained lithium-titanium complex oxides are summarized in Table
1.
[0113] In Table 1, the "Change in paste viscosity" field represents
the difference between the viscosity (Pa-s) of the paste
immediately after its production and that of the paste after having
been let stand for 5 hours, at a sheer speed of 1 (1/s).
TABLE-US-00001 TABLE 1 Li/Ti Element Amount of ratio K P Value per
S CO.sub.2 Change in (measured Percent Percent (K2p peak area
S.sub.SK)/ Equation Percent generation paste Capacity value) by
mass by mass (Ti2p peak area S.sub.STi) (1) by mass wt ppm
viscosity mAh/g Example 1 0.80 0.01 0.10 0.001 10.0 0.00 1100 -25
162 Example 2 0.80 0.05 0.10 0.006 12.0 0.00 1180 -29 167 Example 3
0.80 0.20 0.10 0.011 5.5 0.00 1270 33 167 Example 4 0.80 0.20 0.10
0.003 1.5 0.00 1000 -20 168 Example 5 0.80 0.25 0.10 0.020 8.0 0.00
2050 -30 169 Comparative example 1 0.80 0.00 0.10 -- -- 0.00 1000
-31 151 Comparative example 2 0.80 0.20 0.10 0.029 14.5 0.00 3700
-75 165 Comparative example 3 0.80 0.14 0.10 0.019 13.6 0.00 3100
-55 152 Example 6 0.76 0.01 0.10 0.001 10.0 0.00 1080 -20 159
Example 7 0.76 0.12 0.10 0.011 9.2 0.00 1190 - 7 161 Example 8 0.76
0.25 0.10 0.019 7.6 0.00 1400 10 163 Example 9 0.84 0.01 0.10 0.001
10.0 0.00 2100 -25 160 Example 10 0.84 0.12 0.10 0.012 10.0 0.00
2300 -30 161 Example 11 0.84 0.25 0.10 0.018 7.2 0.00 2800 36 164
Example 12 0.80 0.12 0.10 0.011 9.2 0.01 90 - 9 166 Example 13 0.80
0.12 0.10 0.010 8.3 0.09 70 28 165 Example 14 0.80 0.12 0.01 0.011
9.2 0.00 1400 -35 159 Example 15 0.80 0.12 0.05 0.012 10.0 0.00
1240 -20 167 Example 16 0.80 0.12 0.15 0.013 10.8 0.00 1390 27 168
Example 17 0.80 0.12 0.23 0.012 10.0 0.00 1600 -28 163 indicates
data missing or illegible when filed
[0114] The above results indicate that an electrode paste
containing a lithium-titanium complex oxide conforming to the
present invention would offer excellent stability over time and
that an electrode made from such paste would have a high
capacity.
[0115] In the present disclosure where conditions and/or structures
are not specified, a skilled artisan in the art can readily provide
such conditions and/or structures, in view of the present
disclosure, as a matter of routine experimentation. Also, in the
present disclosure including the examples described above, any
ranges applied in some embodiments may include or exclude the lower
and/or upper endpoints, and any values of variables indicated may
refer to precise values or approximate values and include
equivalents, and may refer to average, median, representative,
majority, etc. in some embodiments. Further, in this disclosure, an
article "a" may refer to a species or a genus including multiple
species, and "the invention" or "the present invention" may refer
to at least one of the embodiments or aspects explicitly,
necessarily, or inherently disclosed herein. In this disclosure,
any defined meanings do not necessarily exclude ordinary and
customary meanings in some embodiments.
[0116] The present application claims priority to Japanese Patent
Application No. 2011-284288, filed Dec. 26, 2011, the disclosure of
which, including the claims, is incorporated herein by reference in
its entirety.
[0117] It will be understood by those of skill in the art that
numerous and various modifications can be made without departing
from the spirit of the present invention. Therefore, it should be
clearly understood that the forms of the present invention are
illustrative only and are not intended to limit the scope of the
present invention.
* * * * *